Since endorphins play an important role in opiate addiction and mental illness, and since some of their receptors are immediately adjacent to cerebral spinal fluid (CSF) pathways, the regulation of the concentration of endorphins in the CSF is a necessary mechanism to study. The transport activity of the choroid plexus in brain is a major factor in regulating concentration of substance in the CSF, thus the nature of endorphins transport in the choroid plexus will be investigated by three methods, namely (1) incubation of isolated choriod plexus, (2) perfusion of isolated choroid plexus, and (3) ventricular-cisternal perfusion. These three methods can tell us how endorphins are transported, how many transport systems of endorphins are classified, how the transport of endorphins is regulated and to explain the relationship between the transport of endorphins and opiate addiction. These are the objectives of this proposal. The incubation of isolated choroid plexus is simple and provides data of how endorphins are transported, but the direction of transport can be determined with perfusion of choroid plexus. The ventricular-cisternal perfusion provides data not only for the transport activity of choroid plexus but also for other brain tissues, therefore it provides more comprehensive data. These data will answer the questions of our objectives and also they will tell us of the mechanisms of bioavailability of endorphins and other peptides in the CSF.